A metal detectorist who discarded a gold ring in his garage for 40 years after a museum told him it was worthless has discovered its real value is £10,000. Tom Clark, 81, dug up the buried treasure while scanning an area of farmland near Aylesbury, Buckinghamshire, in 1979, then put it inside a metal tin and forgot about it. But the retired leather craftsman came across the rare seal ring eight years ago while sorting through items from his mother's house after she passed away. He got the item valued and was astonished to discover that it was actually a 670-year-old medieval artefact dating back to 1350. It is due to be auctioned off in Derbyshire on Tuesday (Aug 27) and is expected to sell for between £8,500 and £10,000. The turn of events is similar to the plot of BBC sitcom Only Fools and Horses, when brothers Del and Rodney come across a watch in their garage which is then auctioned off for millions of pounds. Mr Clark said: "I had completely forgotten about it. At the time I'd only been metal detecting for 10 years and didn't realise the ring was anything special. It was all twisted and broken when I dug it up." He took the rare ring along with some others to a museum to have them valued at the time, but was told they were all fairly modern. "I put them all in a tin and left them in the garage at my mother's house," he said. "A few months ago, I was sorting through some stuff in my own garage that had come from my mother's house and there it was - the tin with the rings in it." Tom is auctioning off the ring, which is expected to make between £8,500 and £10,000 Credit: Hansons / SWNS/Hansons / SWNS Mr Clark, now a much more experienced collector, said he instantly knew it was a seal ring dating back to the 1300s and would have belonged to someone important given its decoration and quality. He added: "It's rare and elegant. I'd love to know who it belonged to." A Latin inscription on the ring translates as 'I hide the true message'. Mark Becher, Historica expert at auctioneer Hansons, said: "It's a fascinating piece of medieval jewellery and I'm delighted Tom rediscovered again after all these years."